Thanks for your reply. The current Mirror X functionality is mostly sufficient for rectangular slices but for a large number of Polygons it requires a lot of fiddly work to get a symmetric result. Ideally, I think it should be possible to map out one half of the stage, duplicate the Polygons and Mir...

In the Advanced output of Resolume Arena using Mirror X or Mirror Y on polygons merely moves them but does not flip the points of the polygon. I am able to get the desired results by mirroring the polygons, copying the width or height of each individual polygon, Alt dragging them to flip them, then ...